Our studies will be concerned with the biological and immunological properties of the bovine leukemia virus (BLV), its natural mode of transmission, and its role in the pathogenesis of leukemia in cattle. Specific areas of studies will be: 1) Development of new molecular and antigen probes for BLV. 2) Factors controlling the expression of BLV genome in bovine lymphocytes and other cells. 3) Development of more sensitive and practical infectivity assay for BLV. 4) Investigation of the mechanism of transmission of BLV. 5) Further characterization of lymphocyte sub-population present in BLV-infected cattle and their role in BLV leukemogenesis.